FIG. 32 shows the arrangement of a conventional image sensing apparatus.
Reference numeral 11 denotes a zoom lens for enlarging/reducing an image; 12, a focus lens for focusing an image; 13, a CCD for photoelectrically converting an image; 14, an A/D converter for converting an analog signal into a digital signal (image data); 15, a camera signal processing circuit for adjusting a sensed image; 16, a buffer memory for temporarily storing image data; 17, a D/A converter for converting a digital signal into an analog signal; 18, a monitor for displaying a sensed image; 19a, a focus motor for moving the focus lens 12; 19b, a focus motor driver for controlling driving of the focus motor 19a; 20a, a zoom motor for moving the zoom lens 11; 20b, a zoom motor driver for controlling driving of the zoom motor 20a; 21, a zoom encoder for detecting the position of the zoom lens 11; 39, a cam table used to obtain in-focus curve information corresponding to a zoom value; 22, a system controller for controlling the respective circuits; 23, a compression circuit for compressing image data; 24, a recording circuit for recording the compressed image data; and 25, a zoom lever & switch for attaining zoom operation.
Light coming from an object forms an image on the imaging surface of the CCD 13 via the zoom lens 11 and focus lens 12. The image on the imaging surface is photoelectrically converted into an analog signal by the CCD 13, and the analog signal is converted into a digital signal (image data) by the A/D converter 14. The image data undergoes image quality adjustment by the camera signal processing circuit 15, and the adjusted image data is stored in the buffer memory 16.
When a zoom instruction is issued by the zoom lever 25, sw1 and sw2 of the zoom lever 25 detect the depression state to zoom in the tele (T) or wide (W) direction, and the system controller 22 sends a signal to the zoom motor driver 20b in accordance with the detection result so as to move the zoom lens 11 via the zoom motor 20a. Likewise, the system controller 22 acquires in-focus curve information from the cam table 39, and sends a signal to the focus motor driver 19b on the basis of the acquired in-focus information so as to move the focus lens 12 via the focus motor 190a, thus zooming while maintaining an in-focus state.
The image data (digital signal) stored in the buffer memory 16 is converted into an analog signal by the D/A converter 17, and the analog signal is displayed on the monitor 18 such as a liquid crystal display (LCD) or the like.
On the other hand, the image data stored in the buffer memory 16 is compressed by high-efficiency coding in the compression circuit 23, and the compressed image data is recorded on a recording medium by the recording circuit 24.
A compression processing device that performs DCT (discrete cosine transformation)-based high-efficiency coding used in the conventional image sensing apparatus such as a digital video camera or the like will be explained below using FIG. 33.
FIG. 33 is a block diagram showing the arrangement of the compression processing device in the conventional image sensing apparatus.
Reference numeral 26 denotes a block processing circuit for forming DCT blocks; 27, a shuffling circuit for rearranging (shuffling) image data blocks; 28, a DCT processing circuit for computing orthogonal transforms; 29, a quantization processing circuit for quantizing image data; 30, a coding processing circuit for encoding the quantized image data using Huffman codes and the like; 31, a deshuffling circuit for rearranging (deshuffling) the shuffled image data blocks to restore them; and 32, a coefficient setting circuit for setting quantization coefficients in the quantization processing circuit 29.
The image data output from the buffer memory 16 is broken up into blocks each consisting of 8×8 pixels by the block processing circuit 26. Then, a total of six DCT blocks, i.e., four luminance signals and one each color difference signals, form one macroblock. The shuffling circuit 27 shuffles in units of macroblocks to equalize information amounts, and the DCT processing circuit 28 then computes orthogonal transforms. Frequency coefficient data output from the DCT processing circuit 28 are input to the quantization processing circuit 29. A set of coefficient data in units of frequency coefficients are divided by quantization coefficients set by the coefficient setting circuit 32. The set of quantized coefficient data in units of frequency components undergo Huffman coding in the coding processing circuit 30 to be converted into variable-length codes, and the deshuffling circuit 31 restores an original image arrangement and outputs the restored data to the recording circuit 24. In this way, the data size is compressed to about ⅕.
However, since the conventional image sensing apparatus such as a video camera or the like compresses an image after equalizing the entire image, the image quality may drop when the compressed image undergoes high-efficiency coding.